1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to a backlight unit for an liquid crystal display and an LCD device including a backlight unit that effectively controls a temperature of a lamp.
2. Discussion of the Related Art
A general notebook personal computer (NTPC) is small in size so that a user may take advantage of information on the NTPC while the user is on the move. The NTPC uses a liquid crystal display module (LCM) as its display device. The LCM includes a liquid crystal (LC) panel and a driving circuit unit. The LC panel includes two glass substrates having pixels arranged in a matrix and switching elements for controlling signals supplied to the pixels. The driving circuit portion provides the signals to the switching elements, thereby driving the LC panel.
The LCM is a light receiving device that displays images by controlling transmittance of light provided from an outside source. Thus, to provide the light to the LC panel, the LCM requires an additional light source, such as a backlight unit including a lamp.
FIG. 1 is a cross-sectional view of a liquid crystal display module (LCM) according to the related art. The related art LCM includes a liquid crystal (LC) panel 2, a main support 14 in which the LC panel 2 is disposed, a top case 10 that completely covers the main support 14 and partially covers an edge of the LC panel 2, a backlight unit disposed under the LC panel 2, and a bottom case 12 disposed under the backlight unit.
The LC panel 2 includes two substrates and a liquid crystal layer is interposed between the two substrates. Upper and lower polarizers 42 and 40 are arranged on outer surfaces of the two substrates, respectively. Liquid crystal pixels are arranged in a matrix between the two substrates, and each liquid crystal pixel is driven by a thin film transistor.
The top case 10 is curved to cover a side of the main support 14 and the edge of the LC panel 2. The main support 14 and the top case 10 are combined by a screw (not shown). The main support 14, generally, is formed by casting a mold. Recently, the main support 14 has been formed of a metal material having a high heat protection property, such as aluminum (Al), for high brightness televisions or monitors.
The backlight unit includes a lamp 20, a lamp housing 16, a light guide plate 24, a reflector 26, and optical sheets 32, 34 and 36. The reflector 26 is disposed over the bottom case 12. The light guide plate 24 and the optical sheets 32, 34 and 36 are sequentially disposed over the reflector 26. The LC panel 2 is disposed over the optical sheets 32, 34 and 36 in the main support 14.
The lamp 20 emits light, and the lamp housing 16 has an opening and surrounds the lamp 20. The lamp 20 and the lamp housing 16 are disposed at a side of the light guide plate 24 such that the opening of the lamp housing 16 corresponds to the side of the light guide plate 24. The reflector 26 is disposed at a backside of the light guide plate 24. The optical sheets include a diffusing sheet 32, a first prism sheet 34 and a second prism sheet 36. The diffusing sheet 32, the first prism sheet 34 and the second prism sheet 36 are sequentially disposed over the light guide plate 24.
A cold cathode fluorescent lamp is commonly used as the lamp 20. Light emitted from the lamp 20 is provided to the light guide plate 24 through the side of the light guide plate 24 corresponding to the opening of the lamp housing 16. The lamp housing 16 reflects light radiantly emitted from the lamp 20 toward the light guide plate 24. The light guide plate 24 has a flat front side and an inclined rear side. The light guide plate 24 changes linear light from the lamp 20 into plane light. The reflector 26 reflects light passing through the rear side of the light guide plate 24 toward the front side of the light guide plate 24 again, thereby reducing light loss.
Thus, light emitted from the lamp 20 provided to the light guide plate 24, and reflected at the inclined rear side of the light guide plate 24 is uniformly transmitted toward the front side of the light guide plate 24. At this time, light incident on the reflector 26 passing through the rear side of the light guide plate 24 is reflected at the reflector 26, and transmitted to the front side of the light guide plate 24. The light transmitted through the front side of the light guide plate 24 is diffused by the diffusing sheet 32 in all directions. The diffused light is condensed within predetermined angles with respect to a normal line to the LC panel 2, passing through the first and second prism sheets 34 and 36.
The LCM having the above structure may be used as a display device for monitors or televisions, especially, for the display devices that may be driven by high voltage and high current. In this case, temperatures of electrodes at both sides of the lamp 20 increase by about 200 degrees Celsius, thereby thermally damaging elements near the electrodes, for example, the light guide plate 24.